Torque wrench monitor

ABSTRACT

A circuit for providing an indication each time a threaded element has been properly tightened by a power torque wrench. A first switch is actuated upon the initiation of operation of the torque wrench to enable a capacitor to be charged at a predetermined rate. A second switch is responsive to the achievement of a predetermined torque output by the torque wrench to couple the charge across the first capacitor to the base of a transistor through a second capacitor. If the elapsed time between the actuation of the first switch and the actuation of the second switch is greater than a predetermined minimum, the signal coupled to the base electrode of the transistor is sufficient to bias the transistor into conduction to energize a lamp for providing an indication that the bolt has been properly tightened.

United States Patent 1 Wiese et .al.

[ July 23, 1974 TORQUE WRENCH MONITOR [73] Assignee: General MotorsCorporation,

Detroit, Mich.

[22] Filed: July 12, 1973 [21] Appl. No.: 378,664

[52] US. Cl 340/213 R, 340/220, 340/219, 340/267 R, 81/525, 307/272,328/1 [51] Int. Cl. G081! 23/00 [58] Field ofSearchm; 340/213 R, 220,419, 267 R, 340/421; 307/254, 27 2, 278, 308; 328/1,

Primary ExaminerJohn W. Caldwell Assistant Examiner-Richard P. LangeAttorney, Agent, or Firm-Howard N. Conkey 57 ABSTRACT- A circuit forproviding an indication each time a threaded element has been properlytightened by a power torque wrench. A first switch is actuated upon theinitiation of operation of the torque wrench to enable a capacitor to becharged at a predetermined rate. A second switch is responsive to theachievement of a predetermined torque output by the torque wrench tocouple the charge across the first capacitor to the base of a transistorthrough a second capacitor. If the elapsedtime between the actuation ofthe first switch and the actuation of the second switch is greater thana predetermined minimum, the signal coupled to the base electrode of thetransistor is sufficient to bias the transistor into conduction toenergize a lamp for providing an indication that the bolt has beenproperly tightened.

2 Claims, 1 Drawing Figure [56] References Cited UNITED STATES PATENTS2,512,032 6/1950 Mellert 8l/52.5 3,613,017 10/1971 Howells 328/2063,664,186 I 5/1972 Kraus 81/525 representing that the threaded elementbeing tightened has been properly tightened thereby.

' In the operation of a power torque wrench with the objective ofturning down and tightening a threaded element to a specified torque,one of three possible events will occur: the specified torque will neverbe obtained, the specified torque will be arrived at too soon indicatingthat the threaded element has-not been properly turned down by reason,for example, of crossthreading or the cycling of the power torque wrenchon a previously tightened element, and the specified torque will-bereached after a predetermined minimum period of time. In the lastinstance only, the threaded element has been properly tightened. It isthe general object of this invention to provide an indication when athreaded element has been properly turned down and tightened by a powertorque wrench.

It is another object of this invention to provide for a circuit whichgenerates a signal indicating that a specified torque has been achievedby a power torque wrench after a predetermined minimum period of timefollowing the initiation of the operation-of the power torque wrench;

These and other objects of this invention are accomplished by a timingcircuit which is energized upon the initiation of the operation of thepower torque wrench, the timing circuit generating a voltage having amagnitude increasing proportional to time. Upon the achievement of aspecified torque by the power torque wrench, this voltage is coupledthrough a capacitor to the base electrode of a transistor. if theelapsed time between the initiation of operation of the power torquewrench and the achievement of the specified torque exceeds a minimumtime required for the proper tightening of a threaded element, themagnitude of the pulse coupled to the base electrode of the transistorthrough the capacitor is of such a magnitude as to bias the transistorinto conduction. Conduction of the transistor effects the energizationof a lamp to provide an indication that the threaded element has beenproperly tightened.

The objects of this invention may be best understood by the followingdescription of a preferred embodiment and the single figured drawingwhich is an electrical I schematic of the circuit of the preferredembodiment for providing an indication when a threaded element has beenproperly tightened by a power torque wrench.

Referring to the drawing, the circuit for providing an indication when apower torque wrench has properly 'turned down and tightened a threadedelement includesa DC power supply comprised of a DC bat-"regulated'voltage is supplied from across the Zener diode 16. Althoughthe DC power source 10 is shown to include a DC battery 12, it isunderstood that a rectified alternating voltage supply could besubstituted therefor.

A normally open switch 18 is series coupled with a relay coil 20 acrossa Zener diode 16. The normally open switch 18 is mechanically associatedwith the power torque wrench so as to be closed upon the initiation ofoperation thereof. A normally open switch 22 is series coupled with arelay coil 24 across the Zener diode 16. The normally open switch 22 ismechanically associated with the power torque wrench and is responsiveto the torque output thereof so as to be closed when a specified torquehas been reached. A timing circuit includes-a capacitor 26 seriescoupled with a resistor 28 across the Zener diode 16. A set of normallyclosed relay contacts 30 are coupled in parallel with the capacitor 26and are operated by the relay coil 20. A resistor 32 and a set ofnormally closed relay contacts 34 are series coupled across thecapacitor 26. The set of normally closed relay contacts 34 are operatedby the relay coil 24.

When both of the relay coils 20 and 24 are deenergized, the capacitor 26is short circuited by theset of normally closed relay contacts 30 and,consequently, is

- maintained discharged. When the relay coil 20 is energized, the timingcircuit is enabled by the opening of the set of normally closed contacts30 and the capacitor 26 is charged through the resistor 28 at a predetermined rate to generate an output voltage proportional to the elapsedtimefrom the energization of the relay coil 20. Upon a subsequentenergization of the relay coil 24, the set of normally closed relaycontacts 34 are opened to couple the voltage across the capacitor 26 toan input circuit 36 of a PNP transistor 38 through a capacitor 40.

The input circuit 36 is comprised of a resistor 42 coupled between thecapacitor and ground and a diode 44 having its anode coupled to thecapacitor and its cathode coupled to the base electrode of thetransistor 38. The emitter electrode of the transistor 38 is groundedand the collector electrode thereof is coupled to the cathode of theZener diode 16 through a relay coil 46.

An indicating lamp 48 and a set of normally open relay contacts ,50 areseries coupled across the series circuit comprised of the DC'battery l2and the on-off .switch 13. The .set of normally open relay contacts 50are operated by the relay coil 46. I

In operation, the regulated power supply 10 is energized upon theclosure of the on-off switch 13. Thereafter, when operation of the powertorque wrench is initiated to turn down a threaded element, the switch18 is closed to energize the relay coil 20. Energization of the relaycoil 20 opens the set of normally closed relay contacts 30 and thecapacitor 26 begins to charge through the resistor 28. The voltageacross the capacitor increases as a function of the elapsed time fromthe closure of the switch 18. Upon the achievement of a predeterminedtorque output of the power torque wrench, the switch 22 is closed toenergize the relay coil 24. Energization of the relay coil 24 opens theset of normally closed relay contacts 34 to couple the voltage acrossthe capacitor 26 to the series combination of the resistor 32, thecapacitor 40, and the resistor 42.

, The resulting pulse coupled to the transistor 38 through the inputcircuit 36 has a magnitude related to the instantaneous magnitude of thecharge on'the capacitor 26 when the set of normally closed relaycontacts 34 are opened. The values of the resistor 32 and the capacitor40 are such that if the elapsed time from the closure of the switch 18to the closure of the switch 22 is equal to or greater than apredetermined minimum time required for the power torque wrench toproperly turn down and tighten the threaded element to the predeterminedtorque, the magnitude of the charge on the capacitor 26 issuch that themagnitude of the pulse coupled 'to the base electrode of the transistor38 through the'input circuit 36 biases the transistor 38 into conductionto energize the "relay coil 46. For elapsed times less than thepredetermined minimum, the magnitude of the pulse coupled to the baseelectrode of the transistor is insufficient to bias the transistor 38into conduction. Capacitor 26 does continue to charge while switchremains open. However, capacitor 40 is of such a value that it chargesmuch faster than capacitor 26. The voltage drop'across capacitor 40results in a continuously decreasing voltage on the base of transistor38. Thus if relay coil 46 is not energized immediately after switch 34opens, it will not be falsely energized later by the charging ofcapacitor 26. Energization of the relay coil 46 affects the closing ofthe normally open relay contacts 50 to energize the indicator lamp 48 toprovide an indication that thethreaded element has been properly, turneddown and. tightened.

If, after the initiation of the operation of the power torque wrench andthe resultant closure of the switch 18, the predetermined torque isnever achieved, the contact 22 remains in the open position.Consequently, the normally closed relay contacts 34 remain closed and nopulse is coupled to the transistor 38 which remains biased intononconduction to maintain the indicator lamp 48 deenergized. If, afterthe initiation of the operation of the power torque wrench and theresultant closure of-theswitch 18, the predetermined torque is achievedbefore the minimum required elapsed time,

the resultant-pulse coupled to the-base electrode of the transistor 38when the set of normally closed relay gize the relay coils 20 and 24,respectively. The resultant closure of the sets of normally closed relaycontacts 30 and 34 result in the discharge of the capacitors 26 and 40.The cycle is then repeated upon a subsequent operation of the powertorque wrench.

To maintain the indicating lamp 48 energized fora set time periodfollowing the energization thereof, a time delay circuit 51 is provided.The time delay circuit 51 is comprised of a resistor 52, a capacitor 54and a set of normally open relay contacts 56 series coupled between thebase'electrode of the transistor 38 and the cathodeof the Zener diode16. A discharge circuit for the capacitor 54 is comprised of a resistor58 series coupled with a set of normally closed relay contacts 60 acrossthe capacitor 54. The set of nonnally open relay contacts 56 and the setof normally closed relay contacts 60 are operated by the relay coil 46.When the transistor 38 is biased into conduction by the pulse suppliedthereto through the capacitor 40, the resultant energization of therelay coil 46 closes the set of normally open relay contacts 56 andopens the set of nornally closed contacts 60. The capacitor 54 ischarged through the resistor 52 at a predetermined rate. The currentinput to the base electrode of the transistor 38 while the capacitor 54is charging is sufficient to maintain the transistor 38 in conduction tomaintain the lamp 48 energized. After the capacitor 54 is charged,

the transistor 38 is again biased into nonconduction to deenergize thelamp 48. When the transistor 38 is biased into nonconduction, the relaycoil 46 is deenergized to open the set of normally open relay contacts56 and to close the set of normally closed relay contacts 60. Closure ofthe set of normally closed relay contacts 60 operates to discharge thecapacitor 54 through the resistor 58. i

As can be seen-from the foregoing description, a circuit is provided,which gives an indication when a threaded element has been properlyturned down and tightened by a power torque wrench as determined by theelapsedtime between the initiation of the operation of the power torquewrench and the achievement of predetermined torque.

The specific details of the power torque wrench and the various switchesare not set forth in the foregoing description as those details are wellknown to one skilled in theart and can take any one of various forms.For example, the power torque wrench may be driven by any of variousmeans such as by an electrical or pneumatic power. The detaileddescription of a preferred embodiment of the invention for the purposeof explaining the principles thereof is not to be considered as limitingor restricting the invention, since many modifications may be made bythe exercise of skill in the art without departing from the scope of theinvention.

We claim:

1. A circuit for providing an indication when a threaded element hasbeen properly tightened by a power torque wrench comprising: first andsecond bistable switch means, each of said switch meanslbeing shiftablebetween respective first and second states; means responsive tothe'initiation of operation of the power torque wrench for shifting thefirst bistable switch means to itssecond state; a timing'circuit coupledto the first switch means for generating an output voltage having amagnitude related to the elapsed time from the shifting of thefirstbistable switch means to its second state, the magnitude of, thevoltage being a set value after an elapsed time equal to a minimum timerequired for the power torque wrench to properly tighten the threadedelement; means responsive to the achievement of a predetennined torqueby the power torque wrench for shifting the second bistable switch meansto its second state; indicating means; and means coupled to the timingcircuit and the second bistable switch means for energizing theindicating means when the instantaneous magnitude of the output voltagewhen the second bistable switch means is shifted to its second state isequal to or greater than the set value, whereby the energization of theindicating means is an indication of the proper tightening of thethreaded element by the power torque wrench;

2. A circuit for providing an indication when ,a threaded element hasbeen properly tightened by a power torque wrench comprising: a DC powersource; a timing circuit coupled in parallel with the DC power source,the timing circuit including a resistor and a first capacitor coupled inseries; a first normally closed switch means coupled in parallel withthe first capacitor; means responsive to the initiation of operation ofthe power torque wrench for opening the first normally closed switchmeans to enable the first capacitor to be charged by the DC power sourceto a voltage having a magnitude related to the elapsed time from theopening of the first normally closed switch means, the magni tude of thevoltage being a set value after an elapsed time equal to a minimum timerequired for the power torque wrench to properly tighten a threadedelement; a second normally nonconducting switch means, the secondnormally nonconducting switch means being responsive to a voltage signalsupplied thereto having a magnitude equal to or greater than apredetermined bias level for shifting to a conducting state; a secondcapacitor having one side coupled to the second normally nonconductingswitch means; means responsive to the achievement of a predeterminedtorque by the power to or greater than the set value; indicating means;andmeans responsive to the conduction of the second normallynonconducting switch means for coupling the indicating means in parallelwith the DC power source to provide an indication of the propertightening of the threaded element by the power torque wrench.

1. A circuit for providing an indication when a threaded element hasbeen properly tightened by a power torque wrench comprising: first andsecond bistable switch means, each of said switch means being shiftablebetween respective first and second states; means responsive to theinitiation of operation of the power torque wrench for shifting thefirst bistable switch means to its second state; a timing circuitcoupled to the first switch means for generating an output voltagehaving a magnitude related to the elapsed time from the shifting of thefirst bistable switch means to its second state, the magnitude of thevoltage being a set value after an elapsed time equal to a minimum timerequired for the power torque wrench to properly tighten the threadedelement; means responsive to the achievement of a predetermined torqueby the power torque wrench for shifting the second bistable switch meansto its second state; indicating means; and means coupled to the timingcircuit and the second bistable switch means for energizing theindicating means when the instantaneous magnitude of the output voltagewhen the second bistable switch means is shifted to its second state isequal to or greater than the set value, whereby the energization of theindicating means is an indication of the proper tightening of thethreaded element by the power torque wrench.
 2. A circuit for providingan indication when a threaded element has been properly tightened by apower torque wrench comprising: a DC power source; a timing circuitcoupled in parallel with the DC power source, the timing circuitincluding a resistor and a first capacitor coupled in series; a firstnormally closed switch means coupled in parallel with the firstcapacitor; means responsive to the initiation of operation of the powertorque wrench for opening the first normally closed switch means toenable the first capacitor to be charged by the DC power source to avoltage having a magnitude related to the elapsed time from the openingof the first normally closed switch means, the magnitude of the voltagebeing a set value after an elapsed time equal to a minimum time requiredfor the power torque wrench to properly tighten a threaded element; asecond normally nonconducting switch means, the second normallynonconducting switch means being responsive to a voltage signal suppliedthereto having a magnitude equal to or greater than a predetermined biaslevel for shifting to a conducting state; a second capacitor having oneside coupled to the second normally nonconducting switch means; meansresponsive to the achievement of a predetermIned torque by the powertorque wrench for applying the voltage charge on the first capacitor tothe second side of the second capacitor to charge the second capacitorand supply a voltage pulse to the second normally nonconducting switchmeans, the voltage pulse having a magnitude equal to or greater than thepredetermined bias level when the magnitude of the voltage on the firstcapacitor is equal to or greater than the set value; indicating means;and means responsive to the conduction of the second normallynonconducting switch means for coupling the indicating means in parallelwith the DC power source to provide an indication of the propertightening of the threaded element by the power torque wrench.